An example of such a field natural gas dehydrator is disclosed in U.S. Pat. No. 5,766,313 to Rodney Thomas Health and the disclosure therein is specifically incorporated herein by reference thereto. In general, such systems comprise a separator means for receiving the oil and water liquids from “wet” (water vapor laden) gas; and a water absorber means, which employs a liquid dehydrating agent such as glycol, for removing the water vapor from the wet gas and producing “dry” gas suitable for commercial usage. The glycol is continuously supplied by a pump to the absorber means in a “dry” low-water vapor-pressure condition and is removed from the absorber means in a “wet” high-water vapor-pressure condition. The wet glycol is continuously removed from the absorber means and circulated through a reboiler means, which includes a still column, for removing the absorbed water from the glycol and heating the glycol to provide a new supply of hot dry glycol. Heating of the glycol in the reboiler means is generally accomplished through use of a gas burner mounted in a fire tube. The hot dry glycol from the reboiler means passes through a heat exchanger, where the hot dry glycol transfers some of its heat to incoming wet glycol going to the still column. The dry glycol subsequently passes to a dry glycol storage tank. A glycol passage means is provided to enable passage of wet glycol from the absorber means to the reboiler means and to pump dry glycol from the storage tank to the absorber means.
Besides water, the wet glycol going to the still column of the reboiler of the natural gas dehydrator will contain natural gas and absorbed hydrocarbons. A large part of the natural gas flowing with the wet glycol to the still column is the natural gas required to power the glycol pump. The balance of the natural gas and other hydrocarbons are absorbed or entrained into the glycol during the water-absorption step in the absorber means.
On many dehydrators, a volume of natural gas is intentionally induced into the reboiler in order to dry the wet glycol to a higher concentration than can be accomplished by simply adding heat. The process of intentionally inducing a volume of natural gas into the reboiler is referred to as gas stripping.
In the still column of the reboiler of the natural gas dehydrator, the water, natural gas, and other hydrocarbons are separated from the glycol by the pressure reduction from the absorber pressure to approximately atmospheric pressure in the still column and by the application of heat from the burner in the fire tube of the reboiler.
The water, natural gas, and other hydrocarbons contained in the wet glycol stream which are separated in the still column from the wet glycol will be exhausted into the atmosphere through the atmospheric vent on the still column. The hydrocarbon vapors released through the still column of a natural gas dehydrator are air pollutants. Specifically, certain hydrocarbons such as benzene, toluene, ethylbenzene, and xylene, commonly referred to as BTEX have been proven to be carcinogenic.
The gas dehydrator disclosed in U.S. Pat. No. 5,766,313 offers solutions to the problems discussed above but improvements can be made to such a gas dehydrator.